Magnets are used in a variety of ways throughout many industrial segments. In virtually all of these uses, it is advantageous to generate as much magnetic strength (i.e., pull) as possible. This creates problems in that, for the most part, the strength of a magnet is directly proportional to its size. This is because the strength of a magnet at a given distance is dependent upon its gauss and the gradient or change in gauss at that distance. In turn, the gauss of a magnet at a given distance is dependent upon the dimensions or geometry of the magnet.
Various materials are used to generate magnetic fields. These include ceramic, rare earth materials, and the materials included in electromagnets. Ceramic materials alone have a relatively low surface gauss (G) of about 1,500-2,000 G in an open circuit condition as used in an overhead surface magnet. As mentioned above, the gauss at a distance from the surface is dependent upon the dimensions of the magnet. Therefore, in order to generate a deep magnetic field, a large ceramic magnet is needed. Although ceramic magnets are relatively low in cost, it is not realistically possible to build ceramic magnets strong enough in order to generate the depth of field necessary to separate ferrous material located deep within large piles of non-ferrous material as ceramic magnets are not capable of producing a high enough gradient necessary to create the strong magnetic draw.
Unlike ceramic magnets, rare earth magnets have a relatively high surface gauss of up to 5,500 G or more in an open circuit condition. While the gauss at a distance from a rare earth magnet is also dependant upon its dimensions, it is not economically feasible to produce large rare earth magnet as such magnets are in general very expensive in that they cost about 50 times as much as a ceramic magnet of the same volume.
Although ceramic magnets are capable of producing a reasonably high gauss at a distance from the magnet's surface, because of their low surface gauss they are incapable of also producing a high gradient or change in gauss at that distance. Rare earth magnets, however, because of their high surface gauss are capable of producing both reasonably high gauss at a distance from the magnet's surface, and a high gradient. Therefore, a magnet that combined the economical features of ceramic magnets with the magnetic power of a rare earth material would be an important improvement in the art.
When large magnets exhibiting great pulling strength at a distance have been required in the past, the only economical solution has been to use electromagnets. Such magnets, however, possess several shortcomings including the fact that they require a significant amount of electric power and are very heavy. Furthermore, in many instances where the magnetic strength of electromagnets are required neither the electric power necessary for operation nor the capability of supporting the great weight of the electromagnet are available.
Composite magnets utilizing rare earth materials are known from U.S. Pat. No. 4,544,904 (Tarachand). The composite magnet disclosed in Tarachand requires an amount of rare earth material that comprises at least 1/3 of the weight of the entire magnet. Given the cost of rare earth materials, it would not be economical to produce large magnets in the manner disclosed in Tarachand. In fact, Tarachand only utilizes small sections of magnets that must be combined with other sections in order to produce a large magnetic surface area.
Given the shortcomings noted above, a permanent magnet that has great pulling strength at a distance, is economical to build, and is competitive in cost to electromagnets would be a great improvement in the art.